A program display device is connected to a programmable logic controller (PLC) which is a control device and displays information such as a program list stored in the PLC. For example, when a trouble occurs in the control of a device to be controlled by the PLC, an operator performs an operation to display the program list stored in the PLC on the program display device and investigates the cause of the trouble.
To display the program list stored in the PLC on the program display device, first, the program display device acquires the program list from the PLC. The program list is constituted by, for example, a format “command number+device code”.
The program display device converts a command number in the program list into a command name with reference to a command name conversion table provided in the program display device and displays the command name together with a device code. The command name conversion table is a table that defines the association between the command name and the command number. It is possible to identify a command name that corresponds to the command number by searching for a command number in the command name conversion table. Thus, the program list is replaced with a display format of command name format “command name+device number” and is then displayed on the program display device.
However, when the command in the program list does not correspond to the command name conversion table provided in the program display device, it is impossible to display the command on the program display device in the command name format. For example, in some cases, when factory equipment is updated, the PLC is updated to a product with a new version, but the program display device associated with the PLC may not be updated. In this case, there is a problem that the program display device which has not been updated cannot display a new command name in a program list added to the PLC of a new version.
For example, it is assumed that the program display device corresponds to command numbers: 1000h to 1FFFh and the PLC corresponds to command numbers: 1000h to 2FFFh. In this case, a command number 2100h included in the program list of the PLC is not present in the command name conversion table of the program display device. Therefore, the program display device cannot identify a command code corresponding to the command number 2100h. Then, the program display device cannot display a command name corresponding to the command number 2100h and displays, for example, a symbol “???” indicating that the command name is unidentified.
Such problems as described above occur due to a difference in specifications between the PLC and peripheral devices thereof caused by the addition of a new function, such as the addition of a system program of the PLC. As a technique related to the addition of a system program, for example, Patent Literature 1 discloses a programmable logic controller and a logic update support tool of the programmable logic controller in which, when a command to add a system library function group is input from a support terminal device, the support terminal device combines information of function group 1 with information of function group 2 to be added to generate a system library object. Then, the system library object is downloaded to a storage unit of the PLC from which data can be read out only when the system library object is executed as a portion of an object program. Then, the system library object is updated and a PLC application is executed. Therefore, it is possible to perform an operation between the PLC and peripheral devices despite a difference in specifications therebetween.